The present invention relates in general to a display control technology and in particular to a technology well applicable to the liquid-crystal driving method such as a technology effectively usable in a display control circuit of a liquid-crystal driving apparatus for displaying dot-matrix characters.
The conventional liquid-crystal driving apparatus for displaying dot-matrix characters comprises a display RAM unit, referred to hereafter as a DDRAM unit, for storing character codes and character-generator RAM and ROM units, referred to hereafter as CGRAM and CGROM units respectively, for storing character font patterns. A CPU (Central Processing Unit) writes codes of characters for display use into DDRAM addresses which correspond to positions on a liquid-display screen. The CPU also writes any arbitrary font patterns into the CGRAM unit. An operation to control liquid-crystal display is carried out as follows. First of all, a liquid-crystal display controller reads out the code of a character stored in the DDRAM unit at an address corresponding to a display position. The code of a character read out from the DDRAM unit is then used as part of an address of the CGRAM or CGROM unit from which a character font pattern is finally read out for display. Accordingly, in order to display a picture pattern other than the dot-matrix characters such a mark or an icon, it is necessary in the case of this configuration to use part of the CGRAM or CGROM unit for dedicatedly storing picture patterns such as marks and icons. An example of a liquid-crystal driving apparatus, that incorporates CGRAM and CGROM if units, is the LCD-II made by Hitachi, Ltd. For details of the LCD-II, refer to the HD44780 on Pages 1 to 12 of the user""s manual which was published in February 1984.
As the number of picture patterns such as marks and icons increases, however, the sizes of the portions of the CGRAM and CGROM units required for storing the picture patterns such as marks and icons also increase as well. As a result, the portions of the CGRAM and CGROM units originally intended for storing font patterns of dot-matrix characters inevitably decrease. For example, in order to store 30 picture patterns such as marks and icons in a CGRAM unit of a liquid-crystal display controller, an area for storing font patterns of six 5xc3x978-dot characters is required. Accordingly, if the capacity of the CGRAM unit is originally large enough only for storing font patterns of 8 characters, the number of dot-matrix characters, the font patterns of which can be stored in the remaining portion of the CGRAM unit, is reduced to 2. Therefore, the number of character font patterns that can be displayed at the same time is limited. As a result, the display control software becomes complicated.
In order to read out picture patterns such as marks and icons stored in the CGRAM and CGROM units, character codes are also required as well. It is thus necessary to write the required character codes in the DDRAM unit in advance. As a result, the picture patterns are difficult to use.
In addition, the conventional CGRAM and CGROM units are used for storing fonts in character units. Accordingly, display control cannot be carried out individually for a picture pattern that corresponds to a bit because information is not stored in bit units. For example, blink control cannot be done only for a particular picture pattern selected from a plurality of picture patterns stored at the same address in the CGRAM or CGROM unit.
The present invention addresses the problems described above. It is an object of the present invention to provide a liquid-crystal display controller for displaying picture patterns such as marks and icons in bit units independently of the display of dot-matrix characters.
Much like the conventional liquid-crystal driving apparatus described above, in order to display a in dot-matrix character, first of all, a character code is read out from a display-RAM unit which is accessed using a display address. Display addresses are generated one after another incrementally in accordance with display positions. The character code is then used in conjunction with a line address (raster address) for accessing a character-generator RAM unit or a character-generator ROM unit, from which a character font pattern is read out.
When displaying a particular line separately from the above operation, a display address is used for accessing a segment RAM unit, from which display/no-display information is read out. The display/no-display information read out from the segment RAM unit indicates whether or not a picture pattern such as an icon or a mark is to be displayed. As described above, display addresses are generated one after another in accordance with display positions.
The liquid-crystal driving operation for displaying character font patterns and the liquid-crystal driving operation for displaying picture patterns such as marks and icons are carried out on a time-division basis. Therefore, it is possible to display dot-matrix characters and picture patterns such as marks and icons on the same screen independently of the dot-matrix characters being displayed.
In addition to the aforementioned display/no-display information indicating whether or not a picture pattern such as a mark or an icon is to be displayed, information specifying display-control attributes such as blinking and black/white inversion can be stored for each mark and icon. A blinking attribute or the like for a particular picture pattern can thereby be selected from a plurality of pieces of mark/icon information stored at the same address in the segment RAM unit. It should be noted that the attribute information described above is an optional feature which is not absolutely required.
A liquid-crystal display apparatus provided by the present invention comprises a display RAM unit, character-generator RAM and ROM units and a segment RAM unit. Character codes are read out from the display RAM unit at addresses generated one after another incrementally in accordance with display positions. Character font patterns are read out from the character-generator RAM and ROM units locations specified by the character codes read out from the display RAM unit. On the other hand, the segment RAM unit is accessed directly by using the addresses generated one after another incrementally in accordance with display positions. Bit patterns read out from the segment RAM unit are used in the display control of picture patterns such as marks and icons. The character-generator RAM and ROM units and the segment RAM unit are accessed for displaying characters and picture patterns such as marks and icons respectively at their display positions on a time-division basis. Therefore, it becomes possible to display dot-matrix characters as well as picture patterns such as marks and icons on the same screen independently of the dot-matrix characters being displayed.
In addition to the display/no-display information for specifying whether or not a picture pattern is to be displayed, attribute information describing a display method for each picture pattern can be included in the data read out from the segment RAM unit through direct accesses using addresses generated one after another incrementally in accordance with display positions. The additional information allows display control such as blinking individual marks and icons to be carried out.